The present invention relates to a control system of an engine including an engine formed with a cylinder, an intake passage for introducing air into the engine, and an exhaust passage through which exhaust gas is discharged from the engine.
Conventionally, engines are formed with a particular passage communicating an exhaust passage with an intake passage, and perform EGR (Exhaust Gas Recirculation) through this particular passage. In the EGR, EGR gas that is a portion of exhaust gas in the exhaust passage is recirculated back to the intake passage and a cylinder.
For example, JP2009-209809A discloses an engine for premixing fuel and air, and causing a resultant mixture gas to self-ignite. In the engine, EGR is performed to introduce an inactive gas into a cylinder, so as to extend an ignition delay time of the mixture gas. Thus, mixing of the air and the fuel is stimulated.
The EGR gas passes through the particular passage and the intake passage, and then is introduced into the cylinder. Therefore, in a case where an increase of an EGR ratio that is a ratio of the EGR gas with respect to all gas in the cylinder is requested, a time delay occurs until the EGR ratio actually increases. For this reason, in a transition state of the engine, the EGR ratio may not suitably be increased and the mixture gas may not suitably combust. For example, in the transition state, if the EGR ratio does not reach a target value and the amount of EGR gas becomes insufficient, pre-ignition of the mixture gas may occur and cause combustion noises, smoke production increases, etc. In this regard, in order to avoid an unsuitable combustion (e.g., pre-ignition), it may be considered to reduce the fuel supply to the cylinder until the EGR ratio rises up to a suitable value. However in this case, engine responsiveness, such as acceleration performance, degrades.